During degassing tests of equipment under vacuum, it is desirable to be able to check the end of the passive or active degassing of the equipment in order to decide on the advisability of terminating or extending the duration of the test, or to check that the equipment desorption rate has reached an acceptable level. Checking the end of degassing generally consists in ensuring that the mass of particles degassed by the equipment and collected on a given surface indicated by the dedicated measurement sensor no longer varies over time despite the persistence of the vacuum. The only apparatus known for such measurements is the quartz crystal microbalance, which measures the mass of a deposit on the quartz crystal from the resulting change in the quartz resonance frequency. The measurement taken is very precise, but the data that the quartz crystal microbalance serves to obtain are only satisfactory if the mass of the deposit collected is very low, typically less than about a hundred micrograms per cm2, so that when a clearly identified substance is deposited as a uniformly ordered layer, it is possible to determine the thickness of the deposit therefrom. The determination of the deposit thickness is only important in the context of the semiconductor industry which must take deposit thicknesses into consideration during metallization, oxidation or epitaxy processes, for example. In this case, the deposit thickness never exceeds a few hundred Angströms. On the contrary, during degassing tests under thermal vacuum, this thickness evaluation is less important and it is more advantageous to quantify the mass of pollutant deposited per unit area at various points of the system under test. For equipment undergoing high degassing under thermal vacuum, such as solar panels, for example, this apparatus is saturated too rapidly due to its high sensitivity. It is then necessary to regenerate it very often by evaporating the deposit collected. The operational limitations engendered by these frequent regenerations make the microbalance unsuitable for most thermal vacuum tests, and especially for those dedicated to the degassing of equipment releasing adhesives and solvents, because they can generate deposits with an order of magnitude evaluated in tens of milligrams per cm2.